1. Field of the Invention
The present invention relates to multilayer packages, and more particularly to multilayer ceramic packages having a stack of layers with ground planes and signal traces coupled to signal vias disposed vertically within the stack.
2. History of the Prior Art
It is known in the art to provide multilayer ceramic packages in which signal traces are interconnected by vertical vias within a stack of layers. The various layers of the packages are provided with ground planes, and the package is typically disposed on a ball grid array (BGA). In addition to the signal vias, the stack is typically provided with a plurality of ground vias which interconnect the ground planes of the stack.
In multilayer ceramic packages of this type, it is frequently necessary or desirable to provide high frequency matching between the signal traces. This is usually accomplished by placing matching stubs alongside the signal traces in the 2-dimentional planar dimensions of the package. A disadvantage of such approach, however, is that it increases the required footprint for the via matching, and therefore results in packages with lower interconnect densities. Moreover, not only is the footprint enlarged by such approach, but matching of broadband bandwidths is more difficult and may require even greater space to accomplish.
The prior art includes various examples of techniques for providing high frequency matching in multilayer ceramic packages. U.S. Pat. No. 6,602,078 of Kwark shows an impedance matching arrangement having a vertical signal line. A ground spacer, together with the signal line and a dielectric medium, form a coaxial structure to provide impedance matching.
U.S. Pat. No. 6,388,208 of Kiani et al. shows a vertical via. Within each of plural layers, there are signal and ground segments. The size and shape of the electrically isolated segments provide an interconnection circuit with a predetermined impedance characteristic.
U.S. Pat. No. 5,830,301 of Sturzebecher, et al. discloses a stack of layers. A cylindrical via is surrounded by an annular dielectric region and outer ground planes are comprised of continuous pairs of ground plane segments.
Other examples in the prior art are provided by U.S. Pat. No. 4,498,122 of Rainal, U.S. Pat. No. 6,172,497 of Okumichi, U.S. Pat. No. 4,851,794 of Williams et al., U.S. Pat. No. 4,494,083 of Josefsson et al., U.S. Pat. No. 6,538,538 of Hreish et al., U.S. Pat. No. 6,072,375 of Adkins et al., U.S. Pat. No. 6,207,903 of Wen et al., U.S. Pat. No. 6,181,219 of Gailus et al., U.S. Pat. No. 6,570,102 of Miller et al., and U.S. Pat. No. 5,801,599 of Flynn et al.
In view of the shortcomings of the prior art, it would be desirable to provide a multilayer ceramic package in which high frequency matching is accomplished by a compact arrangement requiring a small footprint and thereby enabling higher interconnect density in such packages.